Move to SDK EInkDisplay and enable anti-aliased 2-bit text (#5)

* First pass at moving to SDK EInkDisplay library

* Add 2-bit grayscale text and anti-aliased rendering of text

* Render status bar for empty chapters

* Refresh screen every 15 pages to avoid ghosting

* Simplify boot and sleep screens

* Give FileSelectionScreen task more stack memory

* Move text around slightly on Boot and Sleep screens

* Re-use existing buffer and write to whole screen for 'partial update'

src/screens/EpubReaderScreen.h

@@ -20,7 +20,8 @@ class EpubReaderScreen final : public Screen {
 
   static void taskTrampoline(void* param);
   [[noreturn]] void displayTaskLoop();
-  void renderPage();
+  void renderScreen();
+  void renderContents(const Page *p);
   void renderStatusBar() const;
 
  public: